Field of the Invention
The present invention relates to a sensor that generates and detects a terahertz wave, and an information acquisition apparatus using the sensor.
Description of the Related Art
Research and development have been recently performed on application of a terahertz wave (in this specification, an electromagnetic wave of frequency of from 30 GHz to 30 THz) to industrial fields, such as communication, security, and medical. A terahertz wave has penetration capability and rectilinearity, and can acquire inside information of an object with high resolution by reflection signals and transmission signals from the object. Therefore, various nondestructive and noninvasive inspection techniques are developed.
Ultrashort pulse laser or a high intensity magnetic field, an ultralow temperature environment, and the like have been required for generation and detection of the terahertz wave. Therefore, a measuring apparatus for sensing and imaging is large in size and complicated in configuration. As a means to reduce size and weight of such a measuring apparatus, Japanese Patent Laid-Open No. 2006-145513 discloses a generating element that generates a terahertz wave, and an imaging system using a semiconductor diode for a detecting device that detects the terahertz wave. The detecting device detects the terahertz wave penetrated through or reflected on a subject, and acquires a penetration image or a reflection image of the subject. U.S. Pat. No. 7,689,070 discloses a small-sized sensor in which a transmitting unit and a receiving unit of a terahertz wave, and an antenna that combines the terahertz wave and space are integrated and modularized. The sensor improves portability of a measuring apparatus.
The terahertz wave emitted from the transmitting unit may be reflected on an optical member disposed in an optical path between the transmitting unit of the sensor and the receiving unit of the sensor, and may be multiply reflected between the optical member, the subject, and the like. When such a reflective terahertz wave enters a transmitting unit of a small-sized sensor in which semiconductor devices with high coherence property, such as a semiconductor diode, output of the transmitting unit may be destabilized. That is, the reflected terahertz wave may enter the transmitting unit of the sensor and characteristics of the generating element may change, whereby output of the transmitting unit of the sensor may be destabilized.